Watercraft powered by inboard or outboard motors typically include an electrical system. The motor includes a water propulsion device which is powered by an internal combustion engine. As is well known, an ignition system is utilized to fire one or more ignition elements corresponding to each combustion chamber of the engine, igniting the air and fuel mixture in each combustion chamber of the engine.
It is very desirable to keep the engines used in these applications small and simple. To achieve this goal, use of a complex ignition system in which each ignition element is fired and controlled independently may be avoided. In particular, where the engine is of the four-cycle variety, a simple ignition system in which the ignition elements are paired is often used.
In a four-cycle engine, pairs of cylinders are generally arranged so that their pistons are in the same position but out of phase in the operating cycle. In other words, when the pistons corresponding to one pair of cylinders are both at top dead center, one cylinder is in the combustion portion of the cycle, while the other cylinder is in the exhaust portion of the cycle.
In the above-described arrangement where the ignition elements are paired, the ignition elements corresponding to a pair of cylinders are fired at the same time. To accomplish ignition in both cylinders, both ignition elements are fired every half-cycle. This arrangement permits the use of a single coil for both ignition elements, and eliminates the requirement that a separate firing timing signal be calculated and provided for the ignition element associated with each cylinder.
In some situations, it is desirable to disable one or more of the cylinders of an engine without completely shutting down the engine. For example, it may be desirable to disable one or more cylinders to prevent excessive engine speed or reduce engine temperature.
The above-stated ignition system, while being simple, has a drawback associated with a cylinder disabling function. Referring to FIG. 12(b), when it is desired to disable one cylinder, at least two cylinders must be disabled, since the ignition system permits only the turning on and off of the ignition signal associated with the pair of ignition element associated with two cylinders. In addition, if it is desirable to disable more than two cylinders, then four cylinders must be disabled. In the event the engine is of the four cylinder variety, the engine is shut down in this instance.
In either event, the ability of the ignition system to disable cylinders in only pairs can be counterproductive in achieving the goals desired by disabling cylinders. For example, if a slight reduction in engine speed is desired to prevent high engine speed, disabling two cylinders (instead of just one) may cause such a drop in power that the engine stalls or the like. In that instance where the engine is powering a boat, then the user of the boat may be stranded on the water.
An improved ignition system which overcomes the above-stated problems is desired.